This invention relates to linear bearing apparatus for use in moving an object along a rectilinear path with a minimum of friction. More specifically the invention pertains to the combination of a linear bearing assembly and a guide rail therefor, with the linear bearing assembly being of the type incorporating groups of recirculating antifriction balls. The invention also specifically concerns apparatus comprising at least one pair of such recirculating-ball linear bearing assemblies and a pair of guide rails, so constructed and arranged that the direction of action of the load transmitted to the apparatus can be either downward, upward, or opposite lateral directions.
Linear bearings with rolling antifriction balls are finding ever-increasing applications in machine tools and a variety of other pieces of machinery or equipment wherein one part is to be frictionlessly moved back and forth relative to another. As heretofore constructed, however, the linear ball bearings have had drawbacks in connection with the contours of the surfaces defining the ball paths between the bearings and the guide rails. Typical conventional ball paths are, as viewed cross-sectionally, each delineated by four circular arcs arranged like two Gothic arches placed opposite to each other. Each antifriction ball makes contact with the bounding surfaces at four points. This cross-sectional shape of the bottom ball paths is objectionable because of the almost unavoidable slip or spin of the balls under load, giving rise to considerable frictional resistance and uneven wear and so shortening the useful life of the linear bearings.
Additionally, being in contact with the bounding surfaces each at four points, the antifriction balls cannot possibly take up the machining or mounting errors of the other parts of the linear bearings and of the guide rails. For the smooth rolling of the balls, therefore, it has been necessary to machine the parts to the most stringent dimensional tolerances and to mount them in exact positions on other parts of high rigidity which are themselves machined to very close tolerances.